Find First Cell Address
This is a way that I thought up (but I may not be the first)
In B1 enter =IF(A1="","",ROW()) and drag down
Then in C1 enter =ADDRESS(MIN(B:B),COLUMN(A:A)) or =ADDRESS(MIN(B:B),1)
or
For a range such as A1:A100, use this formula
{=CELL("address",INDEX(A1:A100,MATCH(TRUE,A1:A100<>"",0)))}
Must be entered as an array. (Push Ctrl, Shift and Enter simultaneously)